The invention relates to a novel PVC-containing material with a citrate, whose alcohol component contains 2 to 12 carbon atoms.
Polvyinyl chloride (PVC) is one of the economically most important polymers and is widely used as rigid PVC, but in particular as soft or plasticized PVC.
For the production of a plasticized PVC, plasticizers are added to the PVC and the preferred plasticizers are phthalates. Over the last few years phthalates have been increasingly critically evaluated, particularly as a result of their physiological behaviour. Phthalates have a certain stability with respect to physicochemical and biological decomposition reactions. Admittedly the acute toxicity of phthalates is generally low, but the preponderantly used nonyl, decyl and undecyl phthalates have a carcinogenic, teratogenic and embryotoxic action in high dosages in rats and mice. Due to their poor decomposition behaviour phthalates are in particular concentrated in the hepatic tissue of the body.
The physiologically hazardous nature of phthalates in conjunction with PVC is more particularly encountered in their joint combustion products. As a result of the content of aromatic hydrocarbons the combustion products produce a large amount of soot and dioxin formation is also aided by the presence of chlorine. Moreover, high smoke densities occur due to the frequently necessary use of antimony trioxide. Carbonate-based fireproofing agents, which can also reduce a critical hydrogen chloride emission, do not act very effectively, because the necessary quantities mare so large that there is a significant deterioration to the physical property values excluding a use of carbonates.
It is only possible to a limited extent, for the same reason, to use hydroxides such as e.g. aluminium hydroxide and magnesium hydroxide, which also give a lower smoke density in the case of a fire.
The ecologically hazardous nature of phthalate-containing PVC materials is in particular due to poor recycling and disposal behaviour. In the case of disposal in combustion plants the aforementioned high soot proportion and possible dioxin formation give rise to significant problems when using phthalates. With respect to the liberated hydrogen chloride occurring on burning PVC, modern plant designs offer a recycling or reclamation possibility. Due to the stability to microorganisms biological and biochemical decomposition processes are impossible.
Apart from the physiologically and ecologically hazardous nature of phthalate-containing PVC materials, their physical property values also require improvement. In particular, improvements are needed with respect to fogging, i.e. the volatile fraction which the PVC-containing material loses within a certain time at a certain temperature, as well as migration, i.e. the weight loss of PVC-containing material when stored on activated carbon for a certain time at a certain temperature. Embrittlement, low temperature flexibility, burning rate and light fastness are other important characteristic quantities.
DE 35 46 725 C2 and DE 35 20 750 C2 disclose polyvinyl chloride compositions with citrates as plasticizers and processes for the production thereof. Use is exclusively made of citrates in which also the hydroxyl group of the citrate is esterified. The completely esterified citrates are comparatively expensive.
To avoid the above-described risks and disadvantages tests have been carried out for the development of alternative plasticizers and attempts have also been made to develop PVC-free polymers, which can be used without plasticizers.
Significance has been acquired by materials from thermoplastic polyolefins (TPO), and polyurethanes (PUR). The flame resistance setting required in the case of said materials complicated modifications and the production and processing processes were more complicated and costly. In specific cases the end product only contains 50% of the original polymer matrix. Thermoplastic polyolefins and polyurethanes with the necessary characteristics are also roughly twice as expensive as the corresponding PVC products.
Adipates and phosphates were tested as substitutes for the above-discussed phthalates as plasticizer additives for PVC. These esters are free from aromatic hydrocarbons, so that the critical combustion products do not occur. However, these esters have significantly inferior characteristics for important product parameters. In addition their processing is much more difficult and the price is increased compared with phthalate-containing PVC materials.
The problem of the invention is to provide a PVC-containing material, which does not suffer from the prior art disadvantages and which in particular increases the physiological and ecological compatibility, has improved physical characteristics and can be processed with conventional production and processing processes, whilst also being inexpensive.
According to the invention this problem is solved in that the hydroxyl group of the citrate is not esterified.
Compared with phthalates, citrates have an excellent compatibility on being taken up by the organism. The esters are cleaved into the relevant alcohols and the completely unobjectionable citric acid. Thus, there is no concentration in the organism. As there is a freedom from aromatic hydrocarbons, there is also a considerably reduced soot formation. Thus, an important reactant for the particularly critical dioxin formation is missing. Compared with alternative materials a,PVC-containing material has a much better price-efficiency ratio using citrates as the plasticizer additive.
In particularly preferred manner the chain length of the alcohol component of the citrate is in the range C5-C12.
In particularly preferred manner the chain length of the alcohol component of the citrate is in the range C6-C10.
The alcohol component can be branched or unbranched alcohols, optionally also polyfunctional alcohols.
Advantageously the alcohol component of the citrate comprises a mixture of different alcohols with a chain length range of C5-C12.
Particular preference is given to a PVC-containing material, in which the citrate proportion is 35 to 65 wt. %.
Appropriately the PVC-containing material comprises stabilizers with a proportion of 1 to 5 wt. %.
Particularly appropriately the stabilizers comprise calcium/zinc or barium/zinc compounds.
Advantageously the PVC-containing material comprises pigments with a proportion of 0 to 15 wt. %.
In particularly preferred manner the PVC-containing material comprises fireproofing agents in a range 0 to 20 wt. %.
Particularly appropriately the fireproofing agents comprise aluminium and/or magnesium hydroxide. It is obviously also possible to use-other conventional fireproofing agents, such as e.g. antimony trioxide.
Advantageously the PVC-containing material comprises blowing agents, e.g. azodicarbonamide, in a range of 0.1 to 2 wt. %. Other conventional blowing agents can also be used.
The PVC-containing material is in the form of a foam sheet, which can be produced using per se known processes.
In particularly preferred manner the PVC-containing material is in the form of a reinforced foam sheet, which can be produced by coating support materials using per se known processes.
The support material is preferably a textile fabric, knitted fabric, fleece, metal foil and/or sheet and/or foam of other polymer materials.
The PVC-containing material can also be in the form of a rigid moulding, which can be produced using per se known processes.
With respect to the foam sheet, the reinforced foam sheet and the rigid moulding the hydroxyl group of the citrate can be esterified.